With the ceiling in the living room down, we now know why the second floor moves when you walk it. It appears that bath 3 and the master bath upstairs were remodeled at some point in the history of the house — and too much “meat” was cut out of the structure of the house. The joists are severely compromised.
We’re calling in the structural engineer to determine how to best “sister” in new joists to hold the original lumber together and strengthen the second floor. The plumber is also going to have to fix this mess of pipe.